Antti Aarne's theories, enlarged and expanded by American folklorist Stith Thompson in 1961 and by Hans-Jörg Uther in 2004, look at motifs rather than actions – for example, "a soldier makes a deal with the devil" or "a soldier marries the youngest of three sisters".
He criticized Aarne's work for ignoring what motifs did in a tale, and analysed the basic plot, or action, components of Russian folk tales to identify their simplest irreducible narrative elements.
His Morphology of the Folktale was published in Russian in 1928 and influenced Claude Lévi-Strauss and Roland Barthes, though it received little attention from Western scholars until it was translated into English in the 1950s.
In Afanasyev's collection of Russian fairy tales, Propp found a limited number of plot elements or "functions" that constructed all.
He derived thirty-one generic functions, such as "a difficult task is proposed" or "donor tests the hero" or "a magical agent is directly transferred".